The present invention relates to brazing presses for brazing together two or more metal plates to obtain a stratified metal structure, more particularly it relates to presses for brazing together a first work-piece or pressing comprising a plane central portion and a peripheral curved or raised portion, and a second workpiece or cladding covering or lining the central part and at least partially the peripheral part of the first workpiece.
Such brazing presses are generally used in the manufacture of cooking vessels where it is advantageous to join together a drawn workpiece or pressing made, for example, of stainless steel and having a flat bottom and raised and curved side walls, and a workpiece so-called heat-diffusing cladding consisting of a good heat-conducting metal such as copper, aluminium or their alloys.
United States Patent to Dallet & al. filed July 13, 1970, Ser. No. 54.281 and patented Sept. 28, 1971 with the U.S. Pat. No. 3,609,277, assigned to the present assignee, discloses and illustrates in FIG. 1 a brazing press for connecting together a pressing or workpiece having raised edges, and a preformed heat-diffusing cladding whose surface facing the pressing also has raised edges matching in shape to those of the pressing. Brazing is effected by means of a single intermediate heating member of ferromagnetic material termed "susceptor" which has a special form, i.e., it comprises a slightly concave thin central part and thick raised edges whose surface facing the heat-diffusing cladding matches with the final outer form this cladding must take after being brazed onto the pressing. Pressure exerted by the press on the edges of the susceptor causes the edges to pivot, owing to the fact that the susceptor is concave, with respect to its center, and thus strongly pushes the raised edges of the heat-diffusing cladding against the facing portions of the pressing.
The press disclosed in the patent referred to above also comprises an auxiliary inductor which surrounds the edges of the susceptor, in order to make it possible to braze the peripheral curved parts.
Experience has shown that after a certain number of pressing and heating operations, a susceptor arranged in this way loses its concavity at its central part and it is necessary to remove the susceptor from the press and to re-form it in a correct way by applying, for example, pressure against its center, which results in production being interrupted during the time required for replacing the susceptor with a new one.
Furthermore, French Patent filed on Sept. 16, 1970, National Ser. No. No. 70-33585, in the name of the present Assignees and published on Apr. 29, 1975 under the U.S. Pat. No. 2,105,660, discloses a press for stamping a flat cladding placed onto a pressing having a flat bottom and raised edges so that the plate covers both the bottom and the edges, and for brazing them together. This press comprises a mandrel carrying the drawn workpiece, two coaxial jacks one of which carries at its lower end a rigid block incorporating the main inductor and the central flat part of the ferromagnetic susceptor. The first jack is operated first and presses the plane cladding against the flat bottom of the pressing. The second jack carries at its lower end a cylindrical rigid sleeve or case which surrounds the inductor block. The sleeve carries at its lower end the peripheral annular part of the susceptor, which is distinct from its central part and is designed both to match upon stamping with the periphery of the heat diffusing cladding facing the raised edges of the pressing, and to join them together by means of an auxiliary inductor surrounding the peripheral susceptor part from the outside.
Moreover, United States Patent to Moulin & al. filed on Aug. 16, 1972 under Ser. No. 281,763 and patented on Aug. 21, 1973 with U.S. Pat. No. 3,754,109, assigned to the present assignee, also discloses a brazing press for joining a preformed heat-diffusing cladding to a pressing or stamped workpiece for covering the flat bottom and the raised edges of it, in which in order to obtain close contact between the raised edges of the pressing and the periphery of the heat-diffusing cladding, supplementary pressure is exerted from below on the edges of the sidewall of the pressing so as to slightly deform it. This is obtained either by resilient means such as springs, or by means of a double-acting press (a press with two jacks). Supplementary pressure exerted on the jacket must be carefully correlated to the limit of elasticity because it is necessary to avoid both permanent deformation of the pressing and insufficient or total lack of deformation, for example, owing to weakening of the springs, the stamped pressing being generally very rigid. This results in an increase in the cost of the installation.